The invention relates to a centrifugal separator with an inlet channel for a flow containing coarse and fine particles, a first outlet channel for a flow containing predominantly coarse particles, a second outlet channel for a flow containing predominantly fine particles and a separator chamber with at least one separator device, wherein the separator chamber connects the inlet channel to the first outlet channel and the second outlet channel, and wherein the inlet channel, the separator chamber and the two outlet channels form a flow path.
The invention further relates to a method for the separation of a flow containing coarse and fine particles with such a centrifugal separator.
Centrifugal separators are devices with which coarse particles (coarse dust) are separated from fine particles (fine dust) in a flow, referred to as a two-phase flow. The particles occur, for example, in a mill for stone coal grinding by comminution of the grinding material and are then conducted to the separator by a carrier gas flow.
A distinction is made between centrifugal separators of static, dynamic, or static-dynamic type. All centrifugal separators have the factor in common that the flow entering by means of the carrier gas is conducted radially from the outside inwards through the separator and is provided with a twist. The separation between coarse and fine dust takes place in this context on the basis of the forces taking effect on the different particles, in particular centrifugal and gravitational forces.
The insufficiently ground coarse dust is screened out and conducted back to the grinding plates via a first outlet channel, which can have a coarse substance backflow cone element. The fine dust, which has been adequately ground is conveyed away via a second outlet channel, which can have one or more dust lines, for example to a burner of a combustion chamber.
Mills with centrifugal separators are known with which the gas flow, encumbered with grinding dust, enriched with buffer gases and vapours from the grinding process, enters the outer separator chamber with a twist applied by the arrangement of nozzles at the nozzle ring of the mill. A large part of the flow rises as far as the separator cover and impinges on it. In centrifugal movements the flow is then conducted to the inner separator chamber on the other side of a louver with fixed fins or blades and to a fin rotor rotating in the inner separator chamber.
In this situation, the louver formed from fixed fins, which traverse the flow path partially or wholly, serves as a separator device. Embodiments without louver fins are also known.
The rotating fin rotor represents a further separator device. The screened coarse dust then slips back between the fixed louver and rotor, via the coarse substance backflow cone element, onto the grinding plate.
A problem with the centrifugal separator described heretofore is that the flow between the inlet channel and the fin rotor still has a relatively high twist, and that, despite the two separator devices, a relatively large amount of coarse dust passes into the area on the other side of the fin rotor. This leads to the fin rotor being subjected to relatively high loadings and the degree of separation and sharpness of separation is reduced. The consequence is a reduced degree of efficiency of the known centrifugal separator.
To improve the degree of efficiency, the principle is known from the prior art, such as from JP 2000-051723 A, of arranging a deflector ring between the louver fins and the fin rotor, through which a part of the twisted flow is deflected. The intention is that the deflection and the resultant turbulences should increase the degree of separation of coarse dust and therefore the sharpness of separation.
Despite the arrangement of such a deflector ring in the separator chamber, the coarse particles, sinking down, continue to be subjected to a twist, are conducted back into the carrier gas flow, and then impose a burden on the rotor. Due to this, as before, a relatively high proportion of fine dust is carried along and conveyed back again, which imposes an additional burden on the internal grinding circuit. The increased milling circuit further leads to increased pressure losses of the system as a whole, which in turn exerts a negative effect on the smooth running of such a mill and its degree of efficiency. Moreover, the high loading of the rotor causes coarse dust to be carried out through the second outlet channel.
Taking the prior art described heretofore as a starting point, the present invention is based on the object of providing a centrifugal separator and a corresponding separation method with which the degree of efficiency is improved.